Generally, a flash memory device has a function of electrically erasing all data of a cell at once, and thus is widely used in computers and memory cards. Recently, as use of mobile information devices, such as cell phones, personal digital assistants (PDAs), and digital cameras, is rapidly increasing, the flash memory device, instead of a hard disk, is widely used as a storage device. The mobile information devices require high capacity storage devices in order to provide various functions. Accordingly, a flash memory device that can store multi-bit data of 2 bits or more in one memory cell has being suggested.